1. Field of the Invention
The present invention relates to a spread code generation device for spread spectrum communication and, more particularly, to a spread code generation device applicable to a mobile radio terminal device (hereinafter simply called as a mobile station) or a base station which are effectively utilized in a mobile communication system employing Code Distribution Multiple Access (CDMA) operations such as a personal communication system (PCS), a digital cellular, or the like.
2. Description of the Related Art
A CDMA communication method, one of the spread spectrum communication methods, has been disclosed, for example, in "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System" TIA/EIA/IS-95, July 1993 as a TIA/EIA Interim Standard. According to a device disclosed in the above document, a mobile station and a base station respectively generate three kinds of spread codes for communication constituted of I-phase and Q-phase spread code generators for a spread Quadrature Phase Shift Keying (QPSK), and a code generator for cryptographic scrambling. By transmitting data from an interleaving coder in parallel with I-phase and Q-phase respectively by employing the spread QPSK, an SN ratio of the transmitted signal can be improved by approximately 3 [dB].
The communication device employing the spread QPSK disclosed in the above document, however, unifies two series of data path from the interleaving coder by time dividing with a switch, spreads these data series respectively through spread code generators which are disposed in each I-phase and Q-phase, and transmits them concurrently. Accordingly, the conventional technology requires each of independent code generators for I-phase and Q-phase, which necessitates a hardware design to satisfy the above conditions and further causes a problem that a scale of the device is inevitably enlarged. Also, since a length of the code series generated is inevitably restricted depending upon the series employed in the system, the length can not be determined voluntarily or optionally. Therefore, there also arises a problem that the design of the communication method and system must be done with big restrictions.